At the heart of this question is, "What is the value of the marriage ceremony?"

In the beginning, God created Adam, and from his side, God created Eve whom He brought to Adam to be his wife. As to whether, or not, there was any sort of ceremony marking this, the Bible doesn't say, however, it does say that Eve was Adam's wife. (Genesis 2:22-25, 3:8,17, 20, 21; 4:1)

We see from biblical times that there was a ceremony that marked one's marriage, for all are aware of the event that took place in Cana, in Galilee, when Jesus turned water into wine at a wedding feast. (John 2:1-3)

Just as Christian baptism symbolizes what has taken place in the life of the one being baptized (that they have moved from the camp of unbelievers to the camp of believers) the same is true when one is married. The marriage ceremony is a public testimony that the two who are being married have moved from a life of being single to a life of commitment to one another, as husband and wife, in the bonds of marriage; it's a testimony to the world. It's also important to remember that it is God who has instituted governmental authority within civilized society and we are to obey the governing authorities. (Romans 13:1) Civil government has set forth certain requirements for marriage between a man and a woman and we are to abide by them.